Medical devices may be used to deliver therapy to patients to treat a variety of symptoms or conditions. Examples of therapy include electrical stimulation therapy and drug delivery therapy. Examples of symptoms or conditions include chronic pain, tremor, akinesia, Parkinson's disease, epilepsy, dystonia, neuralgia, obsessive compulsive disorder (OCD), depression, sleep dysfunction, urinary or fecal incontinence, sexual dysfunction, obesity, or gastroparesis. Information relating to symptoms or conditions may be sensed by monitoring physiological signals, such as, e.g., electrocardiogram (ECG) signals, electromyogram (EMG) signals, electroencephalogram (EEG) signals, electrocorticogram (ECoG) signals, pressure signals, temperature signals, impedance signals, motion signals, and other types of signals. In some cases, the physiological signals associated with a patient may be relatively low voltage signals that have information encoded at relatively low frequencies in the signal, such as, e.g., brain signals. Detecting information in low voltage and low frequency signals may present significant challenges in medical devices, particularly in the case of implantable medical devices where power resources may be limited.